A. Field of the Invention
The present invention relates to a motor for rotating a disc-shaped information recording medium in a disk drive apparatus. The present invention further relates to a motor for rotating a magnetic recording medium, such as a floppy disk, in a disk drive apparatus.
B. Related Art
Floppy disk drives (hereinafter abbreviated as FDDs) that are commonly used as computer peripheral equipment use a disk having an unformatted capacity of about 2 MB per disk. In recent years, disk drives are known which are capable of driving a high-capacity floppy disk having a capacity of more than 100 MB per disk which enable a high data transfer rate.
In general, the bearing of a spindle motor for an ordinary FDD that uses only a disk of about 2 MB is a sintered metal oil-retaining bearing (also called simply a metal bearing or an oil-retaining bearing) which is inexpensive. This bearing is formed by compression-molding and then sintering a copper-type or iron-type metal powder, and is a type of sliding bearing that is impregnated with oil as a lubricant.
FIG. 4 is a conceptual diagram of a conventional spindle motor using a ball bearing. The rotor of this motor is arranged as follows.
As shown in FIG. 4, a rotor magnet 106, which is magnetized in such a manner that N poles and S poles are arranged alternately in the circumferential direction, is bonded to a rotor case 105 that is made of a magnetic material, such as galvanized sheet iron SECC. The rotor case 105 is fixed to a boss 103 by caulking, which is made of brass or a brass-like material. The boss 103 is press fit to a shaft 101, and the shaft 101 is rotatably supported by bearings 107 and 108. To reliably support and chuck a disk, a disk chucking magnet 104 and a disk chucking pin 115 in the rotor are attached to the rotor case 105. To improve slidability at the time of disk chucking, a disk hub seating sheet 102, typically made of ethylene tetrafluoride film, is bonded to the boss 103 with an adhesive.
On the other hand, in the stator of the motor, each iron core 111 formed by laminating magnetic steel sheets, such as silicon steel sheets, is provided with a winding 112. Stator assemblies formed of a laminated iron core 111 and a winding 112 are fixed to a bearing housing 110 so as to be opposed to the magnet 106 in radial directions. The bearing housing 110 is caulked to a motor base 113 that is made of galvanized sheet iron or similar metal.
In this conventional motor, the motor base 113 is a metal circuit board. In addition, the rotor is driven by supplying electricity to the windings 112 via the wiring on the motor base 113, a harness and a drive circuit (both the harness and the drive circuit not shown in FIG. 4).
FIG. 4 illustrates that in this conventional motor, a spacer 109 for determining the bearing position and the bearings 107 and 108 are bonded to the bearing housing 110. A prop 114 for attaching the motor to a high-capacity FDD is caulked to the motor base 113. Although this motor has higher axial deviation accuracy than a conventional motor using the sintered metal oil-retaining bearing, this motor is disadvantageous in cost because of the use of the ball bearing (i.e., bearing 108) which is expensive.
However, the sintered metal oil-retaining bearing cannot be used, in itself, in a high-capacity FDD that is required to have high axial deviation accuracy to cope with a small track pitch. Therefore, a ball bearing (i.e., a rolling bearing) is employed in spindle motors for a high-capacity FDD. Further, it has been found desirable to drive both a lower-capacity FD and a higher-capacity FD with a single drive motor.